1. Field of the Invention
The present invention relates to a p-type nitrogen compound semiconductor including at least one group III element selected from the group consisting of gallium (Ga), aluminum (Al), boron (B) and indium (In), nitrogen (N) and at least one p-type impurity selected from the group consisting of magnesium (Mg), zinc (Zn) and carbon (C) and a method of manufacturing the same.
2. Description of the Related Art
In the fields of short wavelength light emitting devices, environmentresistant devices, high frequency electronic devices and so on, nitrogen compound semiconductors including GaN, an AlGaN mixed crystal, an InGaN mixed crystal and a BAlGaInN mixed crystal are potential materials for making up such devices. In particular light emitting diodes (LED) using such nitrogen compound semiconductors have been practically utilized and received attention. An achievement of laser diode (LD) has been reported as well, raising the expectation for applications to optical disks and so on.
For practical applications of such devices, it is important to efficiently manufacture high-quality nitrogen compound semiconductors to a sufficient degree to be used for such devices. Producing high-quality p-type and n-type nitrogen compound semiconductors is particularly important for optical devices so as to effectively recombine electrons with holes and to efficiently pass a current.
For manufacturing nitrogen compound semiconductors, methods such as metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) may be used. In the MOCVD method, for example, a source gas of group III element such as gallium, aluminum or indium (an organic metal gas) is introduced together with a source gas of nitrogen such as an ammonia (NH.sub.3) gas over a heated substrate to be reacted. A nitrogen compound semiconductor is thus epitaxially grown on the substrate. In the MBE method, corpuscular beams of group III element and nitrogen are irradiated on a substrate for epitaxially growing a group III-nitrogen compound semiconductor.
For producing an n-type semiconductor, a source gas or a corpuscular beam of n-type impurity such as silicon (Si) is introduced together with a source gas or corpuscular beams of group III element and nitrogen. An n-type nitrogen compound semiconductor with high crystallinity and electrical conductivity is thus easily produced. For producing a p-type semiconductor, a source gas or corpuscular beam of p-type impurity such as magnesium, zinc or carbon is introduced together with a source gas or corpuscular beams of group III element and nitrogen for growing a crystal. Carriers are then activated through electron beam irradiation or thermal annealing, for example, if necessary.
Although an n-type group III nitrogen compound semiconductor is easily manufactured, it is difficult to produce a p-type group III-nitrogen compound semiconductor. Another problem is that crystallinity and conductivity thereof are low. Furthermore, the proportion of the composition and p-type impurity concentration are nonuniform in a grown surface of crystal (a surface parallel to a substrate surface). This is because a source gas or corpuscular beam of group III element and a source gas or corpuscular beam of p-type impurity react to each other before reaching the substrate.
It is particularly difficult to produce a p-type AlGaN mixed crystal to which magnesium is added as p-type impurity. The aluminum proportion of such an AlGaN mixed crystal as a mother crystal is significantly low compared to one without magnesium. The electrical property as a p-type semiconductor is significantly reduced as well compared to GaN with magnesium of similar amount. That is, aluminum of group III elements is particularly easy to react to magnesium of p-type impurity.